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GEOL 404: FINAL - LECTURE 10
Sedimentary Basin
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A depression in the crust of the earth, caused by plate tectonic activity and subsidence, in which sediments accumulates
Mechanically, it is formed by deformation of the lithosphere (stretching, cooling, or bending)
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Three Factors of Basins
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1. Basin-forming tectonics
2. Depositional sequences
3. Basin-modifying tectonics
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Sedimentary Basis Stats
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600 sedimentary basins
25% covering 50% of the area are producing petroleum
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Basin Classifications
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More recent have fewer classes, incorporate global source rocks to find "Mega Petroleum Systems"
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Wilson cycle
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sequence of rifting, passive margin formation, subduction and volcanic arc formation, ocean closure, continent-continent collision
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rift basins distinguishing features
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underlain by continental crust
extensional structural styles
rapid syn-rift subsidence
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Rift Basin Depositional History
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Syn-rift rocks: post rift fill is restricted facies, initially non marine that may become marine
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rift basin reservoirs
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equally sandstone or carbonate
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Rift Basin Source Rocks ans Seals
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Source: marine shales
Seals: Evaporites or thick shales
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Rift Basin Traps
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Anticline, combination, or tilted faults
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Rift Basin Geothermal Gradient
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normal to high
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Rift Basin Petroleum and Risk Factors
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Highly facies dependent oil with low to average gas
Risks include small trap size, high thermal gradient, and source rock development
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Intracratonic Sag Basins
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-located in continental interiors
-shallow waters or marine facies
-equally sandstone or carbonate
-source/seal rock - shales
-high gravity crude/ low nat. gas
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Passive (Divergent) Margins
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-Rifted basement beneath thick sediment wedge - start as intracontinental rifts that continue to seafloor spreading
-reservoir - Sandstone, some limestone
-Marine shale source, shale/evaporite seal
-Gas prone, parafinic intermediate gravity crude, aromatic higher gravity in separation stage
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Strike Slip Basins
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-Formed in a variety of settings
-Small, structurally complex
-Best known from intracontinental/continental margin environments
-Can be termed "hot basins" near mantle, cold with no mantle involvement
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some characteristics of stike-slip fault-related basins
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very rapid subsidence
thick stratigraphic section relative to basin area
very rapid deposition
extreme facies variability
time-temperature evolution may not be sufficient for source rock maturation
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backarc & forearc basins
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small, deep, young
immature poorly sorted clastic sediments
shallow to deep volcaniclastic
res - thick sandstone, seal/source - thick, interbedded shale
Mostly parafanic to paranic-nephtenic w/ low natural gas
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Forearc Basin
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A sedimentary basin between the subduction complex and the volcanic arc
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backarc basin
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basin behind volcanic arc
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foreland basin
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underlain by continental crust, bordered on one side by fold-and-thrust belt
-asymmetric in cross section
-depositional history - Early deep water facies, later shallow-marine to fluvial-deltaic facies
-Mostly sandstone reservoirs
Marine Shale source, shale/evaporite seal
-Mixed crude oil, deeper gas
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Downwarp foreland basin depositional history
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MIxed interfingering shallow marine facies, either carbonate or clastic prone
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Craton margin foreland basin depositional history
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1st cycle mature platform sediments,
2nd cycle organic clastics
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Oil and Gas in Middle East
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Three quarters of world oil reserves
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